This invention relates generally to ignition electrode assemblies for gas-fired oven burners, and more particularly to an electrode assembly whose electrode unit projects through a bushing in the cover plate in the wall of the oven and is pivoted therefrom whereby the tip at the free end of the unit is swingable from a pre-set first position in which the tip is spaced from the gas-emitting port of the burner to define a spark gap therebetween to sustain a spark discharge to a second position in which the tip is in direct contact with the port to initiate the spark discharge.
U.S. Pat. Nos. 2,715,200 and 3,505,568 J. H. Flynn disclose an ignition electrode unit operable in conjunction with a gas-fired burner which takes the form of an elongated cylindrical casing having a longitudinal slot within which are disposed corrugated metal ribbons forming a port from which the gas is emitted This gas is ignited by an electrical spark discharge which jumps across the spark gap between the tip of the electrode unit and the port ribbons.
The high-voltage for producing the ignition spark is derived from a step-up transformer, the voltage being applied between the electrode and the ribbons. In order to obtain optimum performance, the tip must lie in the diametrical casing plane passing through the burner port and a proper spacing must be maintained between the tip and the port ribbons. But even if the gap is properly set when the electrode unit is initially installed, the tip becomes eroded or dirty or warps with prolonged use, and erratic ignition is encountered, making it necessary to shut down the oven to clean, bend or replace the tip.
When ignition electrode units are used in conjunction with gas-fired burners in baking ovens, still other difficulties are encountered. As pointed out in the Temple U.S. Pat. No. 3,490,856, chains travelling within such baking ovens are usually lubricated with a graphite composition. The graphite tends to collect or deposit on the burner ribbons, and this gives rise to ignition problems.
When ignition is erratic or does not take place as soon as the gas burner is turned on, this results in the emission of unignited gas within the oven and create a dangerous condition; for if ignition occurs only after the oven is filled with unignited gas, it may produce an explosion.
In order to overcome this problem, Temple provides an electrode assembly in which the electrode rod supporting the tip is rotatable, making it possible from an external point to manipulate the tip so that it wipes the port ribbons and thereby dislodges the graphite therefrom. In this arrangement, the electrode tip moves in an arc which intercepts the diametrical casing plane passing through the port; hence when the electrode is displaced from this plane to establish a spark gap, this gap will not lie in the diametrical plane but will be displaced therefrom, as a consequence of which optimum gap conditions do not obtain.
In the arrangements disclosed by the Flynn and Temple patents, the oven wall cover plate on which the ignition assembly is supported is provided with a sight hole through which one can observe the spark gap to see whether proper ignition has taken place. But in these patents, the arrangement is such that the electrode assembly projecting into the oven is supported by means of a bracket attached to the burner casing. This brakcet is interposed in the optical path between the sight hole and the spark gap and therefore interferes somewhat with the view of the gap.